The present invention relates to a device for controlling the flow rate of a fuel gas/air mixture, and/or the ratio between the fuel gas and the air in such a mixture. The device includes a housing or body that is provided with an air inlet, a fuel gas inlet, a fuel gas/air mixture outlet, a gas-control passage that is variable by control means for controlling the flow of gas through the device, and an adjustable air-control passage for adjusting the flow of air through the device.
Conventional devices for fuel gas/air mixture control, such as that disclosed in West German Offenlegungsschrift No. 31 20 637-Korsmeier et al dated Dec. 16, 1982; belonging to the assignee of the present invention, comprise hollow tubular control means which may be rotated and moved in the axial direction in a tubular body. The rotation of the control means changes the diameter of the orifice of the gas inlet in the body of such a device, with this orifice communicating with the space within the control means. An air inlet spaced relative to the gas inlet in the axial direction of the body is also arranged in the body of said device. If the control means is moved inside said body, the diameter of the gas orifice and the diameter of an air orifice connecting the air inlet with the annular space between the control means and the body are changed simultaneously. The space within the control means and the annualar space communicate near that end of the control means that faces the end of said body from which the mixture is discharged, with the gas and the air combining only where the spaces communicate and forming a gas/air mixture only at that point. The known device was created for the controlled mixing of the two fluids entering the device at a pressure above atomospheric pressure and being discharged from the device for being conveyed further as a mixture. If the device is used for obtaining and controlling a fuel gas/air mixture, for example for a naturally or self-aspirating gas engine that draws air and fuel gas through the device at a pressure below atmospheric pressure by sucking the fuel air/gas mixture from the fuel gas/air mixture outlet of the device, the negative pressure at the air orifice may be substantially equal to the negative pressure at the mixture outlet, but the negative pressure at the gas orifice may be different due to a certain pressure drop in the gasway between the gas orifice and the gas outlet of the space within the control means attributable to certain features of the design such a device, said pressure difference between the gas orifice and the air orifice affecting the formation of the mixture in the event of changes in the negative pressure. To blend the gas flowing from the gas orifice through the inner space of the control means, and the air flowing separately from the air orifice through the annular space between the control means and the body of the device, at the gas outlet of the control means where the gas and the air combine, a mixing device comprising baffle plates or the like is provided as the fuel gas/air mixture outlet of the known device. Mixing air and gas with said mixing device consumes energy, thereby causing a pressure drop which must be added to the pressure drop across the air and the gas orifices.
It is an object of the present invention to provide a device for controlling the flow rate of a fuel gas/air mixture, and/or the ratio between the fuel gas and the air in the mixture, wherein the negative pressure at the air passage and at the gas passage will be the same when the fuel gas/air mixture is sucked from the mixture outlet of the device and the diameter of the gas-control passage and the diameter of the air-control passage are changed, and which will not consume energy by mixing the two gaseous fluids in a separate mixing device.